As the footprint of electronic components continues to decrease, enabling greater numbers of components to be placed on a printed circuit board (PCB), efficiently dissipating heat produced by the components becomes more challenging. This problem is amplified as even more of these PCBs are housed within a single enclosure, or chassis.
Traditionally, air is used as the catalyst for dissipating heat and cooling the electronic components electronics within the enclosure. But as the performance demands of these electronic components continues to increase, the traditional heat dissipating approaches become more inefficient and less effective. This ineffectiveness is particularly true in instances where the chassis is sealed, which is most often the case where the chassis is used as a line replaceable units (LRU).
LRUs are used primarily as modular components on aircraft and typically contain aircraft electronics. Usually, these enclosures are not sealed. Cooling air streams through the enclosure in order to remove heat generated by the electronics inside the enclosure. These LRU's are widely used, for example, in military aircraft applications. The Aeronautical Radio, Incorporated (ARINC) 600 standards specification defines rack and panel sizes, weights, connectors, mounting positions, cooling features, and other characteristics associated with aircraft LRU's. Also, available air mass, according to the size of the LRU, is specified. The air mass is used to cool the electronic devices inside the LRU. FIG. 1, for example, is an illustration of an ARINC 600 LRU enclosure 100, in which embodiments of the present invention may be practiced.
In FIG. 1, the ARINC 600 enclosure includes a front panel 102 and a rear panel 104. As noted above, air masses can be used to cool electronic devices mounted on a printed circuit board (PCB) inside the enclosure 100. The ARINC 600 standards specification also governs drilled holes in a defined area at the bottom of the enclosure 100 (not shown) and drilled holes 106 at a top of the enclosure 100.
During operation, for example, cooling air can be injected into a bottom air inlet area and will stream through the enclosure 100, through the drilled holes 106, and out of the enclosure 100. This process of streaming air through the enclosure 100 removes heat from the electronic devices. This streaming air, however, exposes the electronic devices to an outer, potentially harmful, external environment. This external environment can be detrimental to the operation and reliability of the electronic devices.
For example, filtering of the external air could be deficient such that as the streaming air comes into contact with the electronic devices, the devices can be damaged. Salt filled air, for example, can have a corrosive effect on the electronics. There are many other disadvantages to the cooling mechanics of the conventional ARINC 600 LRU enclosure 100.
An additional disadvantage is that the streaming air must be filtered to a certain level in order to prevent a sandblasting effect on the electronic devices. Also, in the case of eruption of fire inside the LRU enclosure 100, smoke will be distributed along the cooling paths, permitting the fire to expand to other areas within the enclosure 100. These disadvantages can significantly impact performance, reduce the mean time between failure (MTBF) of the electronic devices, and decrease their reliability.